1. Field of the Invention
This invention relates to a power control system for a CDMA (code division multiple access) mobile radio communication network. Also, this invention relates to a method of determining the cell structure of a CDMA cellular mobile radio communication network. In addition, this invention relates to a CDMA cellular mobile radio communication network.
2. Description of the Related Art
In a CDMA (code division multiple access) mobile radio communication network, uplink radio signals transmitted from mobile stations toward a base station use a same frequency band. Accordingly, xe2x80x9cnear-far problemsxe2x80x9d tend to occur. Specifically, the radio signal received at the base station which is transmitted from a mobile station close to the base station significantly interferes with the radio signal transmitted from a mobile station far from the base station. Thus, the powers of the uplink radio signals outputted from the mobile stations are controlled to remove the near-far problems. In general, the power control is designed to equalize the intensities or the levels of uplink radio signals received at the base station. For example, the base station transmits control signals to the respective mobile stations, and the mobile stations adjust the powers of output radio signals in accordance with the control signals respectively. As will be explained later, a prior-art power control system has a drawback.
It is a first object of this invention to provide an improved CDMA power control system.
It is a second object of this invention to provide an improved method of determining the cell structure of a CDMA cellular mobile radio communication network.
It is a third object of this invention to provide an improved CDMA cellular mobile radio communication network.
A first aspect of this invention provides a power control system for a CDMA mobile radio communication network, comprising first means for controlling powers at which downlink pilot signals are transmitted from base stations so that the numbers of mobile stations managed by the respective base stations will be in a predetermined range; and second means for controlling powers at which uplink signals are transmitted from the mobile stations so that communication qualities related to the uplink signals received by the base stations will converge on a predetermined threshold value.
A second aspect of this invention is based on the first aspect thereof, and provides a power control system wherein the first means comprises means for updating the powers at which the downlink pilot signals are transmitted from the base stations when the numbers of the mobile stations managed by the base stations move out of an allowable range.
A third aspect of this invention is based on the first aspect thereof, and provides a power control system wherein the first means comprises means for updating the powers at which the downlink pilot signals are transmitted from the base stations when the communication qualities related to the uplink signals received by the base stations move out of an allowable range.
A fourth aspect of this invention is based on the first aspect thereof, and provides a power control system further comprising third means for setting desired powers of the uplink signals received by the base stations, and wherein the first means comprises means for updating the powers at which the downlink pilot signals are transmitted from the base stations when the desired powers of the uplink signals received by the base stations move out of an allowable range.
A fifth aspect of this invention is based on the first aspect thereof, and provides a power control system wherein the first means comprises means for updating the powers at which the downlink pilot signals are transmitted from the base stations, and the second means comprises means for controlling the powers at which the uplink signals are transmitted from the mobile stations in response to the powers of the downlink pilot signals which are updated by the means in the first means.
A sixth aspect of this invention provides a method of determining the cell structure of a CDMA cellular mobile radio communication network, comprising the steps of (1) updating powers at which downlink pilot signals are transmitted from base stations in response to differences between uplink communication qualities regarding the respective base stations and an average value among the uplink communication qualities regarding the respective base stations; (2) updating desired powers of uplink signals received by the respective base stations in response to the differences between the uplink communication qualities regarding the respective base stations and the average value among the uplink communication qualities regarding the respective base stations; (3) iterating the steps (1) and (2) until the uplink communication qualities regarding the respective base stations are substantially equal to each other; and (4) determining pilot-signal transmission powers and desired uplink received-signal powers regarding the respective base stations by executing the steps (1), (2), and (3).
A seventh aspect of this invention is based on the sixth aspect thereof, and provides a method further comprising the steps of calculating differences between a threshold value for powers of pilot signals received by mobile stations and lowest values of powers of pilot signals received by the mobile stations, and updating the pilot-signal transmission powers in the base stations in response to the differences between the threshold value for the powers of the pilot signals received by the mobile stations and the lowest values of the powers of the pilot signals received by the mobile stations.
An eighth aspect of this invention is based on the sixth aspect thereof, and provides a method further comprising the steps of calculating numbers of base stations connecting with the respective base stations, calculating differences between an average number of connecting mobile stations per base station and the numbers of the base stations connecting with the respective base stations, and updating the pilot-signal transmission powers in the base stations in response to the calculated differences between the average number of connecting mobile stations per base station and the numbers of the base stations connecting with the respective base stations.
A ninth aspect of this invention is based on the sixth aspect thereof, and provides a method further comprising the step of updating positions of the respective base stations in response to the differences between the uplink communication qualities regarding the respective base stations and the average value among the uplink communication qualities regarding the respective base stations.
A tenth aspect of this invention is based on the sixth aspect thereof, and provides a method further comprising the steps of making a simulation model on the basis of a predicted distribution of mobile stations and measured values of signal propagation characteristics, and executing the steps (1), (2), (3), and (4) with respect to the simulation model.
An eleventh aspect of this invention is based on the sixth aspect thereof, and provides a method further comprising the steps of measuring the communication qualities related to the uplink signals received by the base stations, and executing the steps (1), (2), (3), and (4) in the base stations.
A twelfth aspect of this invention provides a CDMA cellular mobile radio communication network comprising base stations; mobile stations; first means provided in the base stations for measuring uplink communication qualities regarding the respective base stations; second means for updating powers at which downlink pilot signals are transmitted from the base stations in response to differences between the uplink communication qualities regarding the respective base stations and an average value among the uplink communication qualities regarding the respective base stations; third means for updating desired powers of uplink signals received by the respective base stations in response to the differences between the uplink communication qualities regarding the respective base stations and the average value among the uplink communication qualities regarding the respective base stations; and fourth means for causing the second means and the third means to iterate the updating until the uplink communication qualities regarding the respective base stations converge on the average value among the uplink communication qualities regarding the respective base stations, and thereby for determining pilot-signal transmission powers and desired uplink received-signal powers regarding the respective base stations.
A thirteenth aspect of this invention is based on the twelfth aspect thereof, and provides a CDMA cellular mobile radio communication network further comprising a control center connected to the base stations and calculating the average value among the uplink communication qualities regarding the respective base stations.
A fourteenth aspect of this invention is based on the twelfth aspect thereof, and provides a CDMA cellular mobile radio communication network further comprising fifth means for causing the second means and the third means to execute the updating when the number of the base stations is changed.
A fifteenth aspect of this invention is based on the twelfth aspect thereof, and provides a CDMA cellular mobile radio communication network further comprising fifth means for calculating differences between a threshold value for powers of pilot signals received by mobile stations and lowest values of powers of pilot signals received by the mobile stations, and sixth means for updating the pilot-signal transmission powers in the base stations in response to the differences between the threshold value for the powers of the pilot signals received by the mobile stations and the lowest values of the powers of the pilot signals received by the mobile stations.
A sixteenth aspect of this invention is based on the twelfth aspect thereof, and provides a CDMA cellular mobile radio communication network further comprising fifth means for calculating numbers of the base stations connecting with the respective base stations, sixth means for calculating differences between an average number of connecting mobile stations per base station and the numbers of the base stations connecting with the respective base stations, and seventh means for updating the pilot-signal transmission powers in the base stations in response to the calculated differences between the average number of connecting mobile stations per base station and the numbers of the base stations connecting with the respective base stations.
A seventeenth aspect of this invention provides a CDMA mobile radio communication network comprising at least one base station; mobile stations connectable with the base station; first means provided in the base station for transmitting a downlink signal at a variable power; second means for detecting the number of the mobile stations currently connecting with the base station; and third means for decreasing the power, at which the first means transmits the downlink signal, as the mobile-station number detected by the second means increases.